Question: Rewrite ${\dfrac{7^{-9}}{7^{-7}}}$ in the form ${7^n}$.
Explanation: ${ \dfrac{7^{-9}}{7^{-7}} = 7^{-9-(-7)}} $ ${ \hphantom{\dfrac{7^{-9}}{7^{-7}}} = 7^{-2}} $